Animals perform much like humans in many psychoacoustic capacities. However, several tasks reveal striking differences between animals and humans. Animals are markedly inferior to humans in pure tone frequency discrimination. Animals are deficient in discriminating intensity and duration decrements. Animals are deficient in certain tasks involving octave generalization. On the other hand, parakeets perform better than humans in forward and backward masking tasks. The proposed research will compare humans, macaque monkeys and chinchillas in processing simple tones, musical tones, animal sounds, and speech sounds, with emphasis on those tasks for which animals have been shown to be markedly inferior (or superior) to humans. All species will be tested using the same stimuli, procedures, and threshold criteria. Both go, no-go discrimination and left/right identification procedures will be used. Monkeys and chinchillas will be trained with operant conditioning techniques and food reinforcement. The specific objective is to precisely define similarities and differences in human, non-human primate, and non-primate mammalian hearing, in order to determine which species are adequate models for human auditory capacities. The ultimate goal is to integrate existing psychoacoustic data from humans, monkeys, chinchillas and birds in order to more clearly delineate which aspects of human hearing are inherited from vertebrate, mammalian or primate ancestors, and which are species- specific to humans.